Baking vs texture image
If you use an image texture alone for your object, plugged into a diffuse or emission shader - that is as simple as it can be already. Baking is done to get complex information from a shader tree and multiple textures summed up in a few textures that can then be plugged into a Principled Shader. 

If you are only needing the color information from the image texture you already have, baking isn't necessary.